Introduction
The tracking of population health is an essential component of effective public health practice. However, given the many gaps in our current understanding of the role of the environment in disease, the Commission was faced with a fundamental yet vexing question: “What health endpoints should be tracked?”
To address this question, a stepwise approach was undertaken to evaluate available national data to identify health endpoints that may be appropriate for inclusion in a National Environmental Health Tracking Network. The three-step approach included the following:
An examination of national environmental release data to identify broad categories of health effects that may be related to those pollutants released in large quantities.
An evaluation of current agency activities and the scientific literature to identify specific health effects that have been related to environmental exposures and may serve as environmental health indicators.
An analysis of available national level health outcome data for selected endpoints to identify those with high or increasing prevalence or responsible for heavy utilization of health care.
The following sections describe the approach and findings.
An Examination of Environmental Releases: the Toxics Release Inventory
The first step in this analysis was to examine what is known about the potential health effects of pollutants that are released to the environment in large amounts. The EPA Toxic Release Inventory (TRI) is an example of an effective and publicly accessible hazard tracking program. The TRI contains data on annual releases of over 644 toxic chemicals to the air and water by the nation’s major industries. Each year, every covered facility reports the total amount of each chemical released. These data are publicly available and posted on the Internet, providing communities with information about the nature and magnitude of pollution in their neighborhoods.
The Commission analyzed the 1997 TRI data, aggregated nationally to examine total releases and identify the types of health effects that may be related to pollutant-specific exposures. Based upon the volume of total releases and toxicological and epidemiological data compiled by EPA and Environmental Defense, 11 broad categories of possible health effects5 were identified and ranked.(US Environmental Protection Agency, 1999), (Environmental Defense Fund, 2000)
5
This analysis includes both suspected and recognized toxicants. An agent is listed as a recognized toxicant if it has been studied by national or international authoritative and scientific regulatory agency hazard identification efforts. Suspected agents are included if they are shown to have target organ toxicity in either humans or two mammalian species by a relevant route of exposure.
Table 8 lists the total pounds of each class of toxicants released to the air and water based upon the Environmental Defense's Scorecard database. Substances with potential respiratory effects were released in the largest amount in 1997. Neurotoxicants and skin toxicants were next highest in total pounds released. Other categories included developmental, reproductive and endocrine effects.
Table 8: Ranking of Toxicants based on 1997 Toxic Release Inventory (TRI)
Types of health effects Ranking based on total 1997 TRI release
Total Air & Water Releases (Pounds)
Respiratory 1 1,248,977,984
Neurologic 2 1,211,458,945
Skin or sense organ 3 1,109,718,312 Gastrointestinal or liver 4 1,086,264,404 Cardiovascular or blood 5 823,375,664 Developmental 6 811,686,192 Reproductive 7 498,142,705 Kidney 8 488,554,582 Immunological 9 234,713,891 Cancer 10 209,271,142 Endocrine 11 173,331,065
Reference: Environmental Defense Scorecard (www.scorecard.org)
The Commission recognized that this analysis has a number of limitations. Most importantly, the volume released does not indicate the level of actual community exposure. These exposures are not tracked at the community level. In addition, the approach oversimplifies the complex nature of chemical toxicants. Multiple health effects can be associated with an individual toxicant, and complex interactions between toxicants can further impact human health. Also, the TRI is limited to major industrial facilities and does not include all potential sources of these pollutants. Finally, the 644 substances included captures only a fraction of total chemicals in common use potentially released to the environment. Nevertheless, this approach provided the Commission with a starting point for identifying the categories of health endpoints to be considered for tracking. Given the large amount of toxic pollutants released, there is a clear need to improve the tracking of population exposures and to be watchful for any evidence of adverse health impacts.
Identification of Health Endpoints
Step two consisted of a review of the literature, including published work by health and environmental agencies identifying diseases or health endpoints that have been or may be related to environmental exposures. These endpoints are sometimes referred to as environmental health indicators6. At the present time there is strong interest by EPA, CDC and others in developing a
list of environmental health indicators to provide measures of population health that can be related to environmental conditions, providing a public health yardstick for measuring environmental progress.
Table 9 presents a listing of broad categories of health effects and related specific health effects or diseases that have been identified as environmental indicators. The broad categories include those that were identified based upon the TRI environmental release and toxicity data: respiratory, neurological, skin, liver, heart, developmental, reproductive, kidney, and immune conditions, and cancer. This listing also includes an additional listing for birth defects, with multiple references to environmental links. In the previous analysis birth defects were included under the broader definition of developmental effects. The findings also include a number of specific diagnoses or health outcomes such as asthma, chronic obstructive pulmonary disease (COPD), anemias (sickle cell, aplastic), methemoglobinemia, congenital anomalies, low birth weight, spontaneous abortion, diabetes and various types of cancers.
Several of the health endpoints identified in Table 8 are conditions for which environmental exposures have been implicated (Silbergeld, 1994); (Kjellstrom & Corvalan, 1995); (Wills & Briggs, 1995). Others include pre-existing health conditions that may be exacerbated by exposure to environmental pollutants (Kelsall, Samet, Zeger, & Xu, 1997); (Rios, Poje, & Detels, 1993).
The list also reflects agency priorities, including ATSDR’s seven broad categories of priority health conditions, and the HHS Healthy People Objectives community and environmental health indicators (Healthy People 2000 and 2010). Although this list of health endpoints is culled from numerous sources with diverse criteria, the categories and endpoints generally correspond with the target organ effects identified in the previous TRI analysis.
at the World Health Organization (Corvalan & Kjellstrom, 1995); and the Community Health Improvement Process (Institute of Medicine, 1997).
Table 9: Health Endpoints Identified as Environmental Indicators
Broad Category of Health Outcomes Specific Health Outcomes References 1
Diseases of Respiratory/Lung 2, 3, 6
Asthma 2, 3, 4, 5, 7
Chronic obstructive pulmonary disease (COPD)
1, 2, 3
Neurological Disorders 5, 6
Skin Disorders Dermatitis, dermatosis 4
Chronic Liver Disease and Cirrhosis 1, 2
Diseases of the Heart 1, 2, 3
Diseases of the Blood or Blood Forming System
Sickle cell anemia 2
Aplastic anemia 4
Methemoglobinemia 7
Congenital anomalies 1, 4, 6, 7
Birth Defects
Low birth weight 4, 5, 7
Developmental Disabilities 7 6 Reproductive Disorders Spontaneous abortions 4 Kidney Diseases 2, 6, 7 Immune Disorders 6 Malignant Neoplasms Leukemia Lung Kidney Bladder Liver Stomach Upper GI Prostate Skin 1, 4, 6, 7
A Look at National Health Outcome Databases
The third step in the process of identifying appropriate endpoints for environmental health tracking was to examine the available information on those diseases that may be linked to the environment. In order to investigate trends and public health impacts of the identified list of environmental health endpoints, the Commission reviewed a number of national health outcome databases. There is virtually no comprehensive national tracking of these diseases (excepting cancer). However, three data sets based on national survey data provided useful insights into some of these endpoints. Data from the following surveys conducted by the CDC National Center for Health Statistics are presented in the following analysis:
The National Health Interview Survey (NHIS)
The National Hospital Discharge Survey (NHDS)
The National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Medical Care Survey (NHAMCS) (National Center for Health Statistics, 1996)
Initially the analysis was intended to be limited to environmental health outcomes that are clinically observable and classifiable by ICD-9 codes7, and that have been linked to identifiable exposures to environmental agents. Table 10 and Table 11 are examples of such health outcomes identifiable by ICD-9 codes and implicated environmental (or occupational) agents for the categories of respiratory and neurological toxic effects, respectively. Because of the limitations of the available survey and emerging interests in a broader range of health endpoints, the analysis includes a number of endpoints without known environmental causes. Inclusion of a disease in this analysis is not meant to imply environmental etiology. Given the present limitations of knowledge, even in most cases where an environmental exposure has been shown to contribute to the development of adverse effects, it is not possible to quantify the proportion of risk attributed to the environment.
7 The ICD-9 is an acronym for the International Classification of Diseases, 9th Revision. It is a statistical
classification system that arranges diseases and injuries into groups according to established criteria. These codes, which consist of 3-4,and 5-digit classifications, are revised every ten years by the World Health Organization. Annual updates are published by the Health Care Financing Administration (HCFA) (U.S.Public Health Service & Health Care Financing Administration, 1998)
Table 10: Lung and Respiratory Diseases with Indication of Environmental Etiology
Lung and Respiratory Diseases ICD-9 Reference Implicated Environmental Agents
Chronic Sinusitis 473 3 Atmospheric changes
Allergic Rhinitis 477 Pollen 477.0 Allergen 477.8 Chronic Bronchitis 4911Cr VI Emphysema 492 1Chlorine Asthma 493
Chronic airway obstruction, not elsewhere classified 495 2 Organic Allergens
Coal worker's pneumoconiosis 500 2 Coal dust
Asbestosis 5012 Asbestos
Pneumoconiosis due to other silica or silicates 502 2 Silica
Pneumoconiosis due to other inorganic dusts 503 Inorganic dusts
Pneumonopathy due to inhalation of other dust 504 Other dusts
Pneumoconiosis, unspecified 505
Respiratory conditions due to chemical fumes and vapors 506 2 Oxides of metals
Pneumonitis due to solids and liquids(Levy – irritant gases) 507 2 Irritant gases
Respiratory conditions due to other and unspecified external agents 508
Postinflammatory pulmonary fibrosis 515 1 Asbestos
Other diseases of the lung 518
Interstitial emphysema 518.1 1 Aluminum abrasives
Acute Edema 518.4 1 Be, HF, O3, Phosgene
Table 11: Neurological Disorders with Indication of Environmental Etiology
Neurodegenerative & Neurotoxic Disorders
ICD- 9 Reference Implicated Environmental Agents Senile and presenile organic psychotic conditions 290 1 Aluminum
Transient organic psychotic conditions, acute delerium
293 1 Hexachlorophene
Encephalitis, myelitis, and encephalomyelitis Toxic encephalitis
323
323.7 1, 2 Carbon tetrachloride, lead, mercury, thallium Other cerebral degenerations
Alzheimer's disease
331
331.0 1 Aluminum
Parkinson's Disease 332 1, 3 Carbon monoxide, cyanide, MPTP Other extrapyramidal disease and abnormal
movement disorders
Other degenerative diseases of the basal ganglia
333
333.0 2 Iron pigments
Spinocerebellar disease Primary cerebellar degeneration
Othercerebellar ataxia
334
334.2 334.3
1 Azide, diphenylhydantoin, lithium, metronidazole
Other diseases of spinal cord Other Myelopathy
336
336.8 4 Radiation
Disorders of the autonomic nervous system 337 1, 4 Arsenic, lead, methyl bromide, thallium,
acrylamide, carbon disulfide, chloroquine, ethylene oxide, platinum, organophosphorus compounds, etc
Other demyelinating diseases of central nervous 341 1 Lysolecithin, telurium, perhexilene, cyanate, amiodarone, gold, carbon monoxide, cyanide.
Migraine 346 2 Alcohol, iodine rich foods
Other conditions of brain Encephalopathy Cerebral edema 348 348.3 348.5 1, 4 Mercury
Ethidium bromide, cuprizone, triethyltin, arsenic, lead thallium
Other & unspecified disorders of the nervous system Other specified disorders of the nervous system, includes toxic encephalopathy
349
349.8
Mononeuritis of upper limb and mononeuritis multiplex
Carpal tunnel syndrome
354
354.0 Occupational, repetitive motion
Inflammatory and toxic neuropathy 357 4 Myoneural disorders
Toxic myoneural disorders
358
358.2
Toxic
Muscular dystrophies and other Toxic myopathy
359
359.4
Toxic
References: 1. (Klassen, 1996); 2. (Anderson et al., 1990); 3. NIEHS http://www.niehs.nih.gov/oc/factsheets/parkinson.htm; 4.
Examination of the National Health Interview Survey
The National Health Interview Survey (NHIS) provides valuable national level information on the prevalence of and trends for some key health outcomes. For example, the Commission report Attack Asthma (Pew Commission, 2000) drew upon NHIS data to describe the dramatic rise is asthma over the past decade. However, NHIS is not designed to specifically address environmentally related health outcomes. Therefore the information on environmental health endpoints is limited, and some categories of endpoints may include endpoints that are not linked to the environment.
Published NHIS estimates for both chronic and acute conditions are available as far back as 1984. Categories of endpoints are grouped by ICD-9 codes8 in a process called the NHIS recode. Depending upon the disease category, these groupings may or may not be specific to environmental health endpoints. In addition, these categories may include a limited number of endpoints and may provide a misleading estimate of the prevalence of disease in the population. For example, the NHIS grouping for neurological diseases includes migraine headaches, but excludes diseases of growing interest such as Alzheimer’s and Parkinson’s diseases, thus resulting in an underestimation of prevalence of neurological diseases in the population. This is a major limitation of the NHIS data set when evaluating disease trends that may be influenced by environmental exposures. On the other hand, respiratory diseases are adequately captured by the NHIS recode. The disease prevalence and incidence rates give an adequate assessment of respiratory conditions with environmental etiology such as asthma and emphysema. More detailed examples of the limitations resulting from the NHIS recode system can be found in Appendix 1.
Figure 5 shows ten-year trend data for the self-reported prevalence of a number of broad categories of health conditions including:
- Respiratory Conditions - Skin Diseases
- Neurological Disorders
- Reproductive and Fertility Conditions - Endocrine and Metabolic Conditions.
An increasing trend in the reported prevalence for all of these categories between 1986 and 1995 in illustrated in figures 6-8. In Figure 6, endocrine and metabolic disorders show the greatest increase (21.7%) followed by neurological (20%) and respiratory diseases (20%). As previously noted, due to the NHIS recodes, these broad categories of health conditions are combinations of conditions, reflecting endpoints with and without known environmental etiologies.
Figure 7 provides a greater level of detail showing the 10-year trends for the specific health outcomes included in these each broad categories of health conditions. Specific diseases with increasing prevalence include:
Endocrine and metabolic diseases
– thyroid disorders 36.3%, diabetes 19.1% Neurological diseases
– multiple sclerosis 21.2%, migraine headaches 26% Respiratory conditions
– asthma 38.6%, chronic bronchitis 15.3% Reproductive conditions
- prostate diseases 48% (non-cancer including hyperplasia, inflammation)
- disorders of female reproductive organs 28.6% ( i.e., ovarian cysts, disorders of the uterus and cervix)
Figure 8 presents baseline prevalence information for 1997 for a number of childhood health conditions. With increasing concerns about the possible relationship between environmental exposures and neuro-developmental disorders in children, NHIS provides important baseline data on outcomes such as attention deficit disorder (ADD) and autism. According to NHIS, ADD currently affects over 5% of all children. Such estimates are limited, reflecting a single survey and self-reporting.
The role of the environment in the prevalence of these health outcomes remains unknown. These data should not be interpreted as an implication of environmental causality. However, the increasing trends in a number of diseases with potential links to environmental exposures underscore the need for improved tracking to increase our understanding of risk factors, identify populations at high risk, and develop coordinated prevention efforts.
Figure 5: Self-Reported Prevalence for Selected Categories of Disease
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995
Year
Respiratory Conditions
Skin Conditions
Endocrine and Metabolic
Nervous System
Figure 7: Percent Increase in Self-Reported Prevalence of Select Categories of Disease 21.7 20.0 19.6 7.3 2.5 0.0 5.0 10.0 15.0 20.0 25.0 Endocrine and Metabolic Disorders
Neurologic Disorders Respiratory Disease Reproductive / Fertility Disorders*
Skin Diseases
Chronic Health Conditions
Percent Change in Rate per 1,000
Percent Change
* Change from 1988 and 1995
Figure 8: Self-Reported Prevalence of Childhood Chronic Health Conditions 52.1 34.0 5.5 3.6 1.7 0.7 0.7 0.5 0.0 10.0 20.0 30.0 40.0 50.0 60.0
ADD Any other
developmental delay
Mental Retardation
Cerebral Palsy Down's Syndrome Muscular Dystrophy
Autism Cystic Fibrosis
Health Condition Rate Per 1,000 Rate *Childhood = <18 years
Examination of Health Care Data
In addition to disease trends, the Commission reviewed health care information from the 1996 National Hospital Discharge Survey (NHDS), National Ambulatory Medical Care Survey (NAMCS) and National Hospital Ambulatory Medical Care Survey (NHAMCS) that related to the environmental health indicators identified in Table 9.
Table 12 provides a summary of the number of hospital discharges, emergency room visits, hospital outpatient care visits and doctor’s office visits for six broad groupings of health outcomes, including:
- Lung and Respiratory Conditions - Neurological Conditions
- Reproductive and Fertility Conditions - Blood Disorders
- Liver Disease
- Cardiovascular Disorders
Specific disease endpoints within these broad classifications are included where information was available.
As expected, cardiovascular diseases required the most health care resources, including over 48 million doctor visits and 4.6 million hospitalizations. Although pollution exposures have been indicated for some types of cardiovascular diseases, many other environmental risk factors, including lifestyle and obesity, have been implicated as contributing causes. Lu ng and respiratory diseases (33.6 million doctor visits and over 3 million emergency room visits) and neurological conditions (8.7 million doctor visits) also required large amounts of health care services. Of all the lung and respiratory health conditions resulting in utilization of the health care system, asthma and chronic bronchitis accounted for largest proportion of hospital, emergency room, outpatient and doctor visits in 1996. Among the endocrine conditions, diabetes resulted in the most health care use (over 15 million physician visits). Of the neurologic conditions requiring health care, a relatively small fraction were due to neuro-degenerative diseases such as senility, cerebral degeneration, Alzheimer's disease and Parkinson's diseases. However, these diseases have a devastating impact on the quality of life and require care that may not be measured by these surveys.
Although limited to populations with access to health care, rates of health care utilization from these databases serve as a proxy for disease impact on society. These measures can inform the decision process of selecting health outcomes for tracking, and provide indications of the potential benefits of prevention.
Table 12: Total Number of Hospital Discharges, Emergency Room, Outpatient, and Doctor Visits in 1996 for Selected Health Outcomes.
Total No. of Hospital discharge
Total No. of Emergency Room visits
Total No. of Outpatient visits
Total No. of Doctor’s visits
Lung/Respiratory 1,307,000 3,072,000 1,911,000 33,586,000 Chronic bronchitis 404,000 276,000 49,000 1,069,000 Emphysema 31,000 17,000 21,000 315,000 Asthma 474,000 1,935,000 903,000 9,051,000 Neurological 502,000 1,149,000 939,000 8,654,000 Senility 70,000 6,000 5,000 165,000 Cerebral Degeneration 36,000 19,000 133,000 414,000 Alzheimer’s 16,000 11,000 84,000 195,000 Parkinson’s 20,000 18,000 36,000 638,000 Immuno/Endocrine Diabetes 503,000 330,000 2,684,000 15,896,000 Lupus 17,000 1,000 36,000 186,000 Reproductive/Infertility 74,000 63,000 296,000 896,000 Blood 272,000 251,000 289,000 3,171,000 Liver 129,000 71,000 83,000 394,000 Cardiovascular 4,628,000 3,109,000 4,125,000 48,251,000
Conclusions from the Examination of Available Tracking Data
This examination was conducted to assist the Commission in developing recommendations for diseases and health outcomes to be included in the Nationwide Health Tracking Network. A step-wise approach was used to identify health effects based upon potential adverse effects of major pollutants and specific diseases or health outcomes linked to environmental exposures. These health outcomes were then examined through available national tracking surveys to identify those that are increasing in prevalence and result in significant use of health care. Based upon the findings the following conclusions are offered.
– Existing toxicological and epidemiological data indicate that a broad range of health effects may be related to exposure to toxic pollutants in the environment.
– While the impact of these pollutants on population health is unknown, available data indicates that a large amount of pollutants with known or suspected toxic effects is released into the environment with no tracking of population exposure levels.